Physical and Chemical Changes Study Guide PDF

physical chemical changes Topics Chemical changes Chemical changes refer to the process in which one or more substances are transformed into new substances with different properties. A chemical reaction is an example of a chemical change. Chemical changes involve the breaking and formation o...

physical chemical changes Topics Chemical changes Chemical changes refer to the process in which one or more substances are transformed into new substances with different properties. A chemical reaction is an example of a chemical change. Chemical changes involve the breaking and formation of chemical bonds. Chemical changes often involve the release or absorption of energy. Chemical changes can be represented by chemical equations. Crystallisation Crystallisation is the process by which a solid substance forms a crystal structure from a solution, typically through the slow evaporation of the solvent. It is an important purification technique used in various industries. The size and shape of crystals formed can be influenced by factors such as temperature, concentration, and rate of evaporation. Crystallisation is used in the production of drugs, food additives, and chemicals. Different substances have different solubilities, which determines their ability to form crystals. Physical changes Physical changes refer to alterations in the structure or appearance of a substance without changing its chemical composition. Physical changes include changes in state, shape, size, and phase. They can be reversible or irreversible depending on the type of change. Examples of physical changes include melting, freezing, boiling, condensation, and sublimation. No new substances are formed during a physical change. Reversible and irreversible changes Reversible changes can be undone, while irreversible changes cannot be reverted back to their original state.  Examples of reversible changes include melting of ice and boiling of water. Irreversible changes result in the formation of new substances, like burning a piece of paper. Reversible changes are often physical processes, while irreversible changes are typically chemical reactions. Understanding the concept of reversible and irreversible changes is essential in predicting the outcome of various reactions. Rusting of Iron Rusting of iron refers to the chemical process where iron gradually deteriorates due to exposure to oxygen and moisture, forming iron oxide. Rusting is an oxidation reaction where iron atoms lose electrons to oxygen atoms. Presence of water acts as an electrolyte, facilitating the flow of electrons and accelerating rust formation. Rust weakens iron structures and reduces their strength over time. Prevention methods include coating iron surfaces with barriers like paint or galvanization. Types of Chemical Reactions Chemical reactions can be classified into five main types: synthesis, decomposition, single displacement, double displacement, and combustion reactions. Synthesis reactions combine two or more substances to form a new compound. Decomposition reactions break down a single compound into its elements or simpler compounds. Single displacement reactions involve an element replacing another element in a compound. Double displacement reactions occur when ions exchange between two compounds to form new compounds. Combustion reactions involve a fuel reacting with oxygen to produce heat and light energy. Key Terms Chemical Properties Chemical properties describe how a substance interacts with other substances to form new substances. Chemical properties include flammability, reactivity, and toxicity. Chemical properties are determined by the composition of the substance's atoms and the arrangement of its molecules. Chemical properties help identify and classify substances. Chemical properties can be used to predict the behavior of a substance in various reactions. Chemical reaction A chemical reaction refers to the process where substances, also known as reactants, transform to create new substances, known as products. Chemical reactions often involve energy exchange, occurring when bonds break and new ones form. Reaction rate can be influenced by temperature, concentration, and catalysts. Each reaction is represented by a balanced chemical equation, showcasing atom conservation. Reactions can be categorized into numerous types, including combination, decomposition, displacement, and redox reactions. Combination Reaction A combination reaction occurs when two or more substances combine to form a single product, often resulting in a more complex compound. This type of reaction is also known as a synthesis reaction. It typically involves the transfer or sharing of electrons. Energy is usually released in the form of heat or light during a combination reaction. Examples include the combustion of methane and the formation of water. Copper nitrate Copper nitrate is a compound composed of copper, nitrogen, and oxygen. It is often used in laboratories for various experiments and as a catalyst. Copper nitrate has a blue-green color and is soluble in water. It is a strong oxidizing agent and can be hazardous if handled improperly. When heated, copper nitrate can decompose exothermically, releasing toxic fumes. This compound is commonly used in the production of other copper compounds or as a dye for ceramics. Decomposition reaction A decomposition reaction is a type of chemical reaction where a compound breaks down into simpler substances. Decomposition reactions are often initiated by heat, light, or electricity. The reactant in a decomposition reaction is usually a single compound. Decomposition reactions can be classified into thermal decomposition, electrolytic decomposition, and photolytic decomposition. Examples of decomposition reactions include the breakdown of hydrogen peroxide into water  and oxygen, and the decomposition of limestone in the lime kiln. Displacement reaction Displacement reaction occurs when a more reactive element displaces a less reactive element in a compound, resulting in the formation of a new compound with the displaced element. Displacement reactions are also known as redox reactions or single replacement reactions. The more reactive element is usually a metal that displaces the less reactive metal in a compound. The reactivity series helps determine the order of displacement reactions. Displacement reactions are commonly used in various industries, such as the extraction of metals from their ores. Endothermic Reactions Endothermic reactions are chemical reactions that absorb heat from the surroundings, resulting in a decrease in temperature. Endothermic reactions require an input of energy to proceed. The reactants in an endothermic reaction have lower energy than the products. Endothermic reactions can be represented by a positive change in enthalpy (∆H). Examples of endothermic reactions include photosynthesis and the reaction between baking soda and vinegar. Exothermic Reactions Exothermic reactions are chemical reactions that release energy in the form of heat. They are characterized by a decrease in enthalpy. Exothermic reactions are often spontaneous, meaning they occur on their own without the need for an external energy source. Common examples of exothermic reactions include combustion reactions, such as the burning of wood or the reaction between hydrogen and oxygen to form water. The energy released during an exothermic reaction can be harnessed and used for practical purposes, such as in power generation or heating systems. Exothermic reactions can be represented by a negative value for the change in enthalpy (∆H), indicating a release of heat energy. Galvanisation Galvanisation is the process of coating iron or steel with a protective layer of zinc to prevent rusting.  Zinc serves as a sacrificial anode, corroding before the underlying metal, enhancing the material's durability. Galvanisation can be done through hot-dip galvanizing, electroplating, or zinc spraying methods. It is commonly used in construction, automotive manufacturing, and other industries to protect metal components. Galvanised steel is known for its resistance to corrosion and is often utilized in outdoor or harsh environments. hydrated iron oxide Hydrated iron oxide is a compound formed when iron reacts with oxygen and water, exhibiting a yellow to orange color. It is commonly known as rust and has the chemical formula Fe2O3·nH2O. Hydrated iron oxide is formed through the oxidation of iron in the presence of moisture or humidity. It is important to prevent the formation of hydrated iron oxide to protect iron-based structures from corrosion. When exposed to air and moisture, iron undergoes oxidation, leading to the formation of hydrated iron oxide. Irreversible change Irreversible change refers to a chemical reaction or process that cannot be undone or reversed, leading to a permanent transformation of substances involved. This type of change is typically accompanied by the formation of new products. Energy is often required to initiate irreversible changes. Irreversible changes are crucial in industrial processes for manufacturing various products. Once an irreversible change occurs, it is not possible to return the system to its original state. Physical Properties Physical properties are characteristics of a substance that can be observed or measured without changing the substance's chemical composition. Examples of physical properties include color, odor, density, melting point, boiling point, and solubility. These properties can be used to identify and classify substances. Physical properties are often measured using various scientific instruments. Physical properties can be influenced by factors such as temperature, pressure, and the presence of impurities. precipitate A precipitate is a solid that forms from a solution during a chemical reaction. Usually result from a double-displacement or metathesis reaction. Can be defined by changes in color, texture or state. Removal from solution commonly involves filtration or centrifugation. Can help identify the presence of certain ions in a solution. Products In chemistry, 'products' are the substances that are formed as a result of a chemical reaction. The reactants are transformed into products during a chemical reaction. The products may have different physical and chemical properties than the reactants. The stoichiometry of a chemical equation indicates the ratio of reactants to products. The yield of products in a reaction can be affected by various factors such as temperature and concentration. Reactants In the context of chemical reactions, reactants are the substances that undergo a chemical change to form new substances. Reactants are present at the beginning of a chemical reaction and are consumed during the reaction. The reactants combined in a chemical reaction can be elements, compounds, or a mixture of both. The reactants are written on the left side of a chemical equation. The reactants determine the type and nature of the products formed in a chemical reaction. Reversible change Reversible change refers to a process where a substance undergoes a transformation that can be reversed, returning the substance to its original state. Reversible changes are typically physical changes, such as melting or dissolving. In a reversible change, the original substance's properties are retained after the change is reversed. This process involves breaking and forming chemical bonds in a reversible manner. Understanding reversible changes is crucial in studying the behavior of matter and its transformations. Rust Rust is the common term for the reddish discoloration or coating formed on iron or steel due to oxidation. It's a type of iron oxide, specifically Fe2O3 nH2O. Occurs via reaction with oxygen and moisture. Accelerated by salt and acidic conditions. Rusting is an example of a redox reaction. silver nitrate Silver nitrate is a compound commonly used in photography and chemical laboratories for its antiseptic properties and as a reagent in various chemical reactions. Silver nitrate is a white crystalline solid that can decompose upon exposure to light. It is soluble in water and forms a clear colorless solution. Silver nitrate is corrosive and can cause burns on contact with skin. It is commonly used in the silver mirror test to identify aldehydes in organic chemistry.